Fix misleading exception message in ParameterMatchers#has_entry

PR: #513

Previously if has_entry was called without any arguments, it raised the
following exception:

    ArgumentError: Too many arguments; use either a single argument
                   (must be a Hash) or two arguments (a key and a value).

lib/mocha/parameter_matchers/has_entry.rb

@@ -42,20 +42,10 @@ module ParameterMatchers
     #
     def has_entry(*options) # rubocop:disable Naming/PredicateName
       case options.length
+      when 0
+        raise ArgumentError, 'No arguments. Expecting at least one.'
       when 1
-        case options[0]
-        when Hash
-          case options[0].length
-          when 0
-            raise ArgumentError, 'Argument has no entries.'
-          when 1
-            key, value = options[0].first
-          else
-            raise ArgumentError, 'Argument has multiple entries. Use Mocha::ParameterMatchers#has_entries instead.'
-          end
-        else
-          raise ArgumentError, 'Argument is not a Hash.'
-        end
+        key, value = parse_option(options[0])
       when 2
         key, value = options
       else
@@ -85,5 +75,24 @@ def mocha_inspect
         "has_entry(#{@key.mocha_inspect} => #{@value.mocha_inspect})"
       end
     end
+
+    private
+
+    # @private
+    def parse_option(option)
+      case option
+      when Hash
+        case option.length
+        when 0
+          raise ArgumentError, 'Argument has no entries.'
+        when 1
+          option.first
+        else
+          raise ArgumentError, 'Argument has multiple entries. Use Mocha::ParameterMatchers#has_entries instead.'
+        end
+      else
+        raise ArgumentError, 'Argument is not a Hash.'
+      end
+    end
   end
 end

test/unit/parameter_matchers/has_entry_test.rb

@@ -92,6 +92,11 @@ def test_should_raise_argument_error_if_no_entries_are_supplied
     assert_equal 'Argument has no entries.', e.message
   end
 
+  def test_should_raise_argument_error_if_no_arguments_are_supplied
+    e = assert_raises(ArgumentError) { has_entry }
+    assert_equal 'No arguments. Expecting at least one.', e.message
+  end
+
   def test_should_raise_argument_error_if_multiple_entries_are_supplied
     e = assert_raises(ArgumentError) do
       has_entry(:key_1 => 'value_1', :key_2 => 'value_2')